Stabilization of polyisocyanates against discoloration

Abstract

Polyisocyanates are stabilized against discoloration by the addition of certain hindered phenols such as o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxyl benzyl phosphonate.

We claim: 
     
       1. A polyisocyanate containing as a stabilizer against discoloration, from about 20 to about 2500 ppm of a stabilizer selected from the group consisting of 1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate,   2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,   3. bis(2- (4-hydroxy-3,5-di-tert-butylphenyl) ethyl)sulfide,   4. octadecyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate, and   
     
     
       5. mixtures thereof. 
     
     
       2. The composition of claim 1 wherein the polyisocyanate is toluene diisocyanate and the stabilizer is present in quantities of from about 50 ppm to about 500 ppm. 
     
     
       3. The composition of claim 2 wherein the polyisocyanate is an 80/20 mixture of 2,4-/2,6-toluene diisocyanate. 
     
     
       4. The process for preparing a polyisocyanate resistant to discoloration upon storage which comprises distilling said polyisocyanate in the presence of at least about 25 ppm of an organic phosphite selected from the group consisting of 1. triphenyl phosphite,   2. diphenylisodecyl phosphite,   3. trisononylphenyl phosphite,   4. trilauryl phosphite, and   5. mixtures thereof; and adding to the resultant distillate a stabilizer selected from the group consisting of     
     
     
       1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonte, 2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,   3. bis(2-(4-hydroxy-3,5-di-tert-butylphenyl)ethyl)sulfide,   4. octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and   5. mixtures thereof; and wherein said stabilizer is employed in quantities of from about 20 ppm to about 250 ppm.     
     
     
       5. The process of claim 4 wherein the polyisocyanate is toluene diisocyanate which is distilled in the presence of from about 50 ppm to about 600 ppm of triphenyl phosphite and the stabilizer is present in quantities of from about 50 ppm to about 500 ppm. 
     
     
       6. The process of claim 5 wherein the polyisocyanate is an 80/20 mixture of 2,4-/2,6-toluene diisocyanate. 
     
     
       7. A polyisocyanate containing as a stabilizer against discoloration from about 10 ppm to about 250 ppm of a mixture comprising A. an organic phosphite selected from the group consisting of 1. triphenyl phosphite,   2. diphenylisodecyl phosphite,   3. trisnonylphenyl phosphite,   4. triisodecyl phosphite,   5. trilauryl phosphite, and   6. mixtures thereof; and     B. a member of the group consisting of 1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate,   2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,     
     
     
       3. bis(2-(4-hydroxy-3,5-di-tert-butylphenyl)ethyl)sulfide, 4. octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and   5. mixtures thereof; and wherein the equivalent ratio of B:A is from about 0.01:1 to about 10:1.     
     
     
       8. The composition of claim 7 wherein the polyisocyanate is toluene diisocyanate and the stabilizer is present in quantities of from about 25 ppm to about 250 ppm. 
     
     
       9. The composition of claim 8 wherein the polyisocyanate is an 80/20 mixture of 2,4-/2,6-toluene diisocyanate. 
     
     
       10. The composition of claim 9 wherein the stabilizer mixture is in an equivalent ratio of (B):(A) of from about 0.35:1 to about 1.45:1. 
     
     
       11. The composition of claim 10 wherein the stabilizer is a mixture of triphenyl phosphite and Component (B-2). 
     
     
       12. The composition of claim 10 wherein the stabilizer is a mixture of triphenyl phosphite and Component (B-3). 
     
     
       13. A process for preparing a polyisocyanate resistant to discoloration upon storage which comprises distilling said polyisocyanate in the presence of at least about 25 ppm of an organic phosphite and adding to the resultant distillate a stabilizer mixture comprising A. an organic phosphite selected from the group consisting of 1. triphenyl phosphite,   2. diphenylisodecyl phosphite,   3. trisnonylphenyl phosphite,   4. triisodecyl phosphite,   5. trilauryl phosphite, and   6. mixtures thereof; and     B. a member of the group consisting of 1. o,o-di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate,   2. tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane,   3. bis(2-(4-hydroxy-3,5-di-tert-butylphenyl)ethyl)sulfide,     
     
     
       4. octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and 5. mixtures thereof; and wherein the equivalent ratio of (B) : (A) is from about 0.01:1 to about 10:1.     
     
     
       14. The composition of claim 13 wherein the polyisocyanate is toluene diisocyanate and the stabilizer is present in quantities of from about 25 ppm to about 250 ppm. 
     
     
       15. The composition of claim 14 wherein the polyisocyanate is an 80/20 mixture of 2,4-/2,6-toluene diisocyanate. 
     
     
       16. The composition of claim 15 wherein the stabilizer mixture is in an equivalent ratio of (B):(A) of from about 0.35:1 to about 1.45:1. 
     
     
       17. The composition of claim 16 wherein the stabilizer is a mixture of triphenyl phosphite and Component (B-2). 
     
     
       18. The composition of claim 16 wherein the stabilizer is a mixture of triphenyl phosphite and Component (B-3).